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Old 12-08-2008, 04:44 PM   #1
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What heat range should I expect from my Furnace?


I have a vent on top of my furnace that is only about 12" above the A-coil from which I thought the temperature of the air coming out would be hotter. I can easily put my hand on the vent with no discomfort. Seems as though the furnace is running considerably longer than it should in my opinion. It meets the required 68 degree temperature as set by the thermostat but for an average work day, runs most of the time that we are home. When not home, the thermostat is set to 62, same as at night.

I'm not currently home but I have put an outside thermometer sensor into this vent to record the highest temperature. (The last I knew, it was around 104 degrees F.) In comparison, I dropped my son of at the sitters today and felt the heat coming out of there closest vent (right next to the furnace) and it was uncomfortably hot for my hand about 8" away.

Which furnace is working properly and the other not? Many thanks for your replies.

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Old 12-08-2008, 06:24 PM   #2
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What heat range should I expect from my Furnace?


What type of furnace do you have? Nat gas, lp., oil ,heat pump etc..
There should be a label that specifies what the temperature rise should be. Temperature rise is the difference between the return and supply air.

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Old 12-08-2008, 06:43 PM   #3
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What heat range should I expect from my Furnace?


How old, is it an 80 or 90% efficient, did you always have this problem? If it's got a lot of turbulence at that point the air won't be warm.

Need the other info before I can get a handle on it.
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Old 12-08-2008, 07:36 PM   #4
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What heat range should I expect from my Furnace?


Sorry about the specifics guys.

It's NG / 92.6 efficient. I believe it's the original furnace to house which was built in the later part of 2000. So about 8 years old. I had the furnaced serviced about this time last year.

This is only our second winter at the house and I don't remember how things were different last year. Nor did I have a previous year to compare to. I have however sealed all the ducts, installed an Aprilaire media air filter, along with an Aprilaire 400A whole house humidifier this year. (Maybe this makes it feel cooler with the bypass unit being right there?)

My thermostat has an "Energy" button that can tell me the number of hours the furnace runs for the day, yesterday, current week, last week, and since last reset.

I'll have to look for the temperature rise on the furnace. I've heard of this for measuring the AC but wasn't aware of it for heat.

Thanks again.
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Old 12-08-2008, 09:23 PM   #5
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What heat range should I expect from my Furnace?


make and model please.

By pass might be pertinent, but that high over the coil i am kinda doubtful.

You may have too large a duct system. or the fan is running too fast, or the gas press is way to low.

I would take a temp reading about three feet out from the furnace in the middle of the trunk.
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Old 12-08-2008, 09:38 PM   #6
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What heat range should I expect from my Furnace?


You may also have a lower BTU furnace than the babysitters. Every house is different.

p.s. Be carefull telling others that you checked your babysitters ducting. Only a qualified HVAC expert is allowed!
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Old 12-08-2008, 09:49 PM   #7
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What heat range should I expect from my Furnace?


smaller furnace or not, 108*F ain't right ...30 degree Delta Tee? that's what it works out with 70*F return air. Either the OP is not reading the temp right or something is in need of remediation.
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Old 12-08-2008, 10:11 PM   #8
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Old 12-08-2008, 10:12 PM   #9
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What heat range should I expect from my Furnace?


Quote:
Originally Posted by hvaclover View Post
How to correctly measure duct temp.
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Old 12-09-2008, 03:23 AM   #10
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What heat range should I expect from my Furnace?


Are you using a different type of air filter this year.

Could be the gas valve is not working right and not allowing enough gas to be burned.
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Old 12-09-2008, 09:57 AM   #11
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What heat range should I expect from my Furnace?


The furnace is a 1993 (house built again in late 2000) Goodman GSM080-4
Temp. Rise 35-65
Designed Max. Outlet Temp. 165 Set limit at 160

Heating Inupt Hi 80.0 Lo 48 MBTU/HR
Output Capacity Hi 72.4 Lo 43.4 MBTU/HR

Could not find just a BTU output reading anywhere. Maybe calculated from the numbers above? House is 2400+ sq. ft. Sitters hours (older couple in their late 60's) have like a 700 sq. ft. home.

Is this furnace big enough for my home?

I had kind of expected immediate temperature output readings in my initial temperature readings. After return back to the thermometer and reading the max output and comparing it again to a complete cycle this morning, the max reading was 120 degrees. Just kind of takes a full cycle to get there.
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Old 12-09-2008, 09:57 AM   #12
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Are you using a different type of air filter this year.

Could be the gas valve is not working right and not allowing enough gas to be burned.
Yes, it was using a 1" thick filter and now I'm using a 4" thick filter.
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Old 12-09-2008, 10:18 AM   #13
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What heat range should I expect from my Furnace?


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Yes, it was using a 1" thick filter and now I'm using a 4" thick filter.
Where are you stuffing this 4 inch filter? If you are restricting the air flow, your burner maybe be cycling off and on by the high limit switch.
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Old 12-09-2008, 10:48 AM   #14
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What heat range should I expect from my Furnace?


It appears you have a 2 stage furnace. When the furnace is in low fire the supply temp. will be lower. The second stage is controlled by a timer built into the circuit board if a 2 stage thermostat is not used. I may be mistaken but I believe that timer may be adjustable so the first stage time can be shortened. This will allow the high fire stage to come on sooner .
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Old 12-09-2008, 11:14 AM   #15
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What heat range should I expect from my Furnace?


Good point, I didnt read the two stage part.

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